Davit, particularly for marine use

ABSTRACT

Davit, or crane, particularly for marine use, wherein the lifting chain is engaged between powered sprockets to be kept taut therebetween and thereby to prevent kinks and entanglements of the chain, and wherein the boom sprocket is of swivel design enabling lateral angularity of the chain during use.

United States Patent Birdwell Jan. 21, 1975 [54] DAVIT, PARTICULARLY FOR MARINE USE 2,249,185 7/1941 Smaltz et a1. 254/175.7

2,279,853 4/1942 White 254/175.7 [76] Inventor. J. C. Birdwell, 8535 Glencrest, 23151628 M1943 Lamond 254/172 Houston, 77.017 2,900,089 8/1959 McIntyre. 212/59 R 2,947,516 8/1960 Jackson 1 254/175.7 [22] m 1973 3,750,970 8/1973 Tremoulet 254 1755 x [21] Appl. No.: 348,996

- Primary Examiner-Evon C. Blunk 7 Assistant Examiner 1ames L. Rowland [52] U.S. C1. 212/1, 212/3, 212/58 R,

7 254MB 254M755, 254/184 Attorney, Agent, or FzrmCarl B. Fox, Jr. [51] IntJCl. .1 B66c 13/10, B66d 1/48 58 Field 01 Search 212/31, 35, 52, 54, 58, 1571 ABSTRACT 212/59, 61, 41, 3, 1, 8; 254/172, 173, 183, Davit, 0r crane, particularly for marine use, wherein 184, 185, 175.7, 139.1, 175.5; 318/6, 7; the lifting chain is engaged between powered sprock- 74/2421 TA, 242.11 C; 91/412 ets to be kept taut therebetween and thereby to pre vent kinks and entanglements of the chain, and [56] References Cited wherein the boom sprocket is of swivel design en- UNITED STATES PATENTS abling lateral angularity of the chain during use.

1,099,645 6/1914 Graham 212/61 X 26 Claims, 4' Drawing Figures 7o as DAVIT, PARTICULARLY FOR MARINE USE BACKGROUND AND SUMMARY OF THE INVENTION The use of chain instead of cable for davits or cranes intended for use in lifting objects disposed beneath the surface of a body of water is preferred, because chain, unlike cable, will drop straight down into the water, whereby it may be directed to a sub-surface location readily without weight being added to its lower end to insure that it will remain straight. Cable, on the other hand, has more or less permanent bends which make it difficult to drop the lower end of a cable to a particular point under water. Cable also tends to become snarled and entangled if it happens to loop around itself or around some object in or near its path beneath the water surface, or thereabove.

Frequently in underwater operations objects must be lifted or pulled sideways, whereby the lifting chain is disposed laterally angularly from the end of the boom to the object, and it is advantageous that the lifting chain be and remain surely engaged with the sprocket over which it is passed at the end of the boom, in order that the chain will not become dislodged from the sprocket or .jammed within the sprocket housing.

While the apparatus is useful in marine installations, it may equally well be employed in dry land installations.

Other objects'and advantages of the invention will appear from the following detailed description of a preferred embodiment of apparatus according to the invention, reference during the description being made to the accompanying drawings.

BRIEF DESCRIPTIONS OF THE DRAWINGS FIG. 1 is a side elevation, partly in vertical cross section, showning a preferred embodiment of apparatus according to the invention.

FIG. 2 is'a plan view of the apparatus shown in FIG. 1.

FIG. 3 is an enlarged partial view, largely in vertical cross section, showing support elements for the apparatus.

FIG. 4 is a schematic flow diagram showing a system for controlling the hydraulic fluid motors employed in the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, and describing the preferred embodiment ofapparatus shown therein, a base ring is suitably supported to bear the weight and operating load of the apparatus. Ring 10 may, for example, be supported upon the deck of a boat or ship, on a dock or wharf, on the bed of a truck, on a stationary floor or platform, or may be supported upon any other surface or structure for use in marine or non-marine service. As shown in the drawings, ring 10 is supported above an opening to the hold of a boat or ship.

An external ring gear 12 is fixedly mounted around the upper side of support ring-10. An outer bearing race 13 is provided around the interior periphery of gear 12. An inner bearing race 14 is provided in ring element 15 which rotates during operation of the apparatus. A plurality of bearing balls 16 are rotatably engaged between bearing races 13, 14, to rotatably support ring element 15. Other forms of bearings, such as LII of upper plate 20, lower plate 21 and circumferential plate 22, suitably welded together. The platform 18 may be internally reinforced as necessary, or may be formed in any other suitable manner. A circumferential ring 24 is fixed to platform 18 and is bolted on top of bearing race ring 15 by a plurality of circularly spaced bolts 25. Platform 18 rotates with ring 15.

Two hydraulic motors 27 and gear boxes 29 are mounted upon supports 28 outwardly extending from the upper side of-platform 18 at each side of the platform. The gears of each gear box 29 connect a hydraulic motor 27 to gear 31 engaged with ring gear 12. Operation of hydraulic motors 27 therefore causes inner bearing race member 15 and platform 18 to be rotated. Hydraulic motors 27 are reversible so that the platform may be rotated in either direction.

The boom 35 is formed of plate elements welded together to form elements of box structure. Boom elements 36, 37 have vertically disposed plates 38, 39 affixed thereto at their inner ends, and plates 38, 39are each disposed between a pair of bracket plates 40 welded or otherwise suitably affixed vertically to plate 20 of platform 18. Pivot pins 41 pivotally connect boom elements 36, 37 to platform 18. The boom also includes a cross element 44 and angular convergingv elements 45, 46' which terminate at tapered ends. A fabricated box-form structure 47 fixed to the outer ends of elements 45, 56 forms the outward terminal porion of boom 35.

An upwardly smaller support structure 48 is formed of welded together angular plates 49-51, vertical front plate 52, and top plate 53. Two pairs of vertical bracket plates 54 are welded atop plate 53, and end plates 57, 58 of hydraulic cylinders 59, 60, respectively, are pivotally connected thereto by pivot pins 61. Hydraulic cylinder rods 63, 64 are connected at their ends 65, 66, respectively, to pivot brackets 67, 68 affixed at the upper inner end of boom end structure 47. Extension of rods 63, 64 causes lowering of the boom, and withdrawal of rods 63, 64 causes raising of the boom.

A chain sprocket 70 is rotatably supported between identical parallel plates 71 (only one being shown) having end plates 72, 73 connecting their opposite ends.

Shafts 74, 75 affixed to plates 72, 73, respectively,.are journaled in bearings 76, 77 which are affixed to the angular bottom of support 81 which is inserted into a rectangular opening 82 through the outer end of terminal boom element 47. Sprocket 70 is driven by hydraulic motor 78, in either direction of rotation. The outwardly extending edges 83 of support 81 are bolted to the boom by bolts 84. An opening 85 is provided through support 81 for inspection of the sprocket therebeneath. The sprocket 70 and bearings 76, 77 may be removed through opening 82 with support 81 as a unit.

Shafts 74, 75 are tubular, and chain 88 extends through shaft 74 to be engaged around chain sprocket 70. The outer end of chain 88 drops vertically downwardly. Chain 88 extends at its inner end under and upwardly around sprocket 9 0 driven by hydraulic motor and gear box assemblies 91, 92 disposed at opposite sides of the sprocket, and chain 88 then extends upwardly around and over sprocket 93 which is driven by hydraulic motor and gear box assemblies 94, 95 disposed at opposite sides of the sproket. From sprocket 93, chain 88 drops downwardly into the hold of the boat or ship. Sprockets 90, 93 and hydraulic motor and gear box assemblies 91-92 and 9495 are supported by a pair of angular plates 97, 98 which are secured to the side of plate 52 of support 48, and to the upper side of platform 18. Plates 97, 98 are disposed at opposite sides of the sprockets 90, 93, and the hydraulic motors are disposed outwardly of the plates at the opposite sides. A pipe 101 is provided through platform 18 through which chain 88 extends into the hold.

The hydraulic system for controlling hydraulic motors 78, 9192, and 94-95, which control sprockets 70, 90 and 93, is shown in FIG. 4 of the drawings, which will be later explained. A tank 103 containing hydraulic fluid is mounted on platform 18, one end extending over bracket 104 affixed to plate 22. Electric drive motor 105, which may instead be a gasoline engine or other suitable motor or engine, is coupled through gear box 106 to hydraulic fluid pump 107 which delivers pressured hydraulic fluid to the hydraulic motors 27. The connecting hydraulic linesare no shown. Their use and function will be well known to persons skilled in the art. A control assembly 109 is positioned opposite the position of tank 103, and control equipment for the apparatus may be installed therein. The control equipment will include electrical, manual, air or hydraulic, or other suitably controls for electric motor 105, and for the other hydraulic equipment. Such apparatus is well known in the art and is not further described or shown in the drawings.

The controls for the hydraulic motors 78, 9l92 and 94-95 are shown in FIG. 4. A pump 115 is driven by electric motor 105 through gear box 106. The electric motor may be driven in either direction of rotation to drive the pump in either direction of rotation. Makeup hydraulic fluid is continuously drawn into the system through conduit 119 from tank 103 or other suitably source, through strainer 120 and filter'12l, by charge pump 122. The hydraulic fluid circulates through the system, so that only the amount necessary to keep the system completely filled is fed in through charge pump 122. Arrows 124 indicate the direction of hydraulic fluid flow for operation of the sprockets to draw in chain 88 from the end of the boom. Arrows 125 indicate the direction of hydraulic fluid flow for paying out the chain from the end of the boom.

Motors 78, 9192 and 94-95 are reversing hydraulic motors. Conduits 127a, 127b deliver hydraulic fluid to all of the hydraulic motors when the chain is to be drawn in, the fluid returning to pump 115 through conduits 128b and 128a. conduits 128a and 128b deliver hydraulic fluid to all of the hydraulic motors when the chain is to be payed out, the fluid returning through conduits l27b and 127a.

In conduit 1281; between its connections to hydraulic motors, 78 and 91 there is provided pressure control valve 130 through which hydraulic fluid will flow in the direction of arrows 124 only when the pressure exceeds a certain magnitude. Since hydraulic motor 78 is held against rotation by the static hydraulic fluid until hydraulic fluid flow therethrough commences, chain 88 is held against movement until that certain magnitude of pressure is reached and hydraulic motor 78 commences to operate. In operationto draw chain 88 in from the end of the boom, pump 115 is operated to pump in the direction of arrows 124 and the pressured hydraulic fluid reaches pump motors 94 and 95 through conduit 127a, pressured fluid also flowing through conduit 127b to hydraulic motors 78, 91 and 92. No hydraulic fluid can flow across hydraulic motor 78 initially because of valve 130. The other hydraulic motors to which hydraulic fluid is delivered are, however, prevented from operating because the chain is held stationary by hydraulic motor 78. Therefore, the chain cannot move at all until the trailing hydraulic motor, the last hydraulic motor in the series with respect to the direction of chain travel, commences to operate. Each hydraulic motor that is receiving pressured hydraulic fluid and is trying to operate, motors 9192 and 9495, pulls with the torque imposed by the hydraulic fluid pressure. Therefore, chain 88 is maintained tensioned until such time as the hydraulic fluid pressure exceeds the magnitude of pressure necessary to pass through valve 130 and the trailing hydraulic motor 78 commences to function. This chain tension is maintained thereafter, after all of the hydraulic motors have commenced operating, because each hydraulic motor maintains its pull or torque and there is no oppurtunity for any slack to delvelop in the chain.

The same condition exists when the chain is to be paid out. In conduit 127a between its connections to hydraulic motors 94 and 95, there is provided pressure conrol valve 132 through which hydraulic fluid will flow in the direction of arrows 125 only when the pressure exceeds a certain magnitude. Since hydraulic motor is held against rotation by the static hydraulic fluid until hydraulic fluid flow therethrough commences, chain 88 is held against movement until that certain magnitude of pressure is reached and hydraulic motor 95 commences to operate. In operation to pay the chain out from the end of the boom, pump is operated to pump in the direction of arrows and the pressured hydraulic fluid travels through conduits 128a and 128b to hydraulic motors 78, 9192 and 9495. No hydraulic fluid can flow across hydraulic motor 95 initially because of valve 132. The other hydraulic motors to which hydraulic fluid is delivered are, however, prevented from operating because the chain is held stationary by hydraulic, motor 95. Therefore, the chain cannot move at all until the trailing hydraulic motor, the last hydraulic motor in the series with respect to the direction of chain travel, commences to operate. Each hydraulic motor that is receiving pressured hydraulic fluid and is trying to operate, motors 78, 9l92 and 94, pulls with the torque imposed by the hydraulic fluid pressure. Therefore, chain 88 is maintained tensioned until such time as the hydraulic fluid pressure exceeds the magnitude of pressure necessary to pass through valve 132 and the trailing hydraulic motor 95 commences to function. This chain tension is maintained thereafter after all of the hydraulic motors have commenced operating, because each hydraulic motor maintains its pull or torque and there is no opportunity for any slack to develop in the chain.

Hydraulic fluid flow through conduit 128b in the direction opposite to the direction of arrows 124 is not impeded by valve 130. Flow through conduit 127a in the direction opposite to the direction of arrows 125 is not impeded by valve 132. Therefore, the hydraulic fluid return flows are unrestricted.

A valve 133 in conduit l27b between hydraulic motors 78 and 91 normally permits unrestricted flow in both directions. Valve 133, however, may be operated to permit equalization of hydraulic motor 78 through cross conduit 134 when chain 88 is not moving and the boom is being raised or lowered. Raising of the boom causes chain tightening between sprockets 70 and 90, and lowering of the boom causes slackening between these sprockets, and in either case pressure equalization across motor 78 is desirable to permit chain tension adjustment.

Relief valve 136 connected through conduit 137 to conduit 128a and through conduit 138 to conduit 127a is provided to vent excess pressure of hydraulic fluid from the system.

As will now be understood, the platform 18 may be rotated so that the direction of the boom can be altered. The boom may be raised and lowered as has already been explained. The chain 88 is kept taut spockets 70 v and 93, and consequently is taut between sprockets 70 and 90 and between sprockets 90 and 93. When the chain is to be lowered from the boom end, sprockets 70, 90 and 93 are driven by hydraulic motors 78, 9l92 and 94-95 in rotational directions corresponding to the direction of the chain travel. A controlled hydraulic drag is imposed between sprockets 70 and 93. The drag effectively maintains a selected minimum tension in chain 88. The tension in chain 88 can be increased or decreased by control of hydraulic fluid supplied to hydraulic motor 78 .and to the hydraulic motors of hydraulic motor-gear box assemblies 94 and 95. When the chain 88 is to be withdrawn from the water or other point of use sprockets 70, 90 and 93 are driven by hydraulic motors 78, 91-92 and 94-95 in rotational directions corresponding to the direction of chain travel. A controlled hydraulic drag is imposed between sprockets 70 and 93. The drag effectively maintains a selected minimum tension in chain 88.

Sprocket 90, the intermediate sprocket, may be not powered at all, with chain tension maintained between sprockets 70 and 93, in either chain travel direction, and sprocket 90 idling. Sprocket 90 may have one or two control valves of the type of valves 130, 132 so that it, too, can function as a chain drag imposing means in either or both directions of chain travel.

Since the chain is kept taut between sprockets 70 and 90 and between sprockets 90 and 93, there is no danger handled at the lower end of the chain may be to the side.

of boom 35, and powered sprocket 70 rotates in bearings 76, 77 so that the ,chain and sprocket remain aligned'at all times. Wear and tear on the chain and sprocket andother equipment is minimized by this arrangement. v

A counterweight 111 is affixed to the side of the assembly including sprocket 70 at the side opposite hydraulic motor 78 to counterbalance the weight of hydraulic motor 78.

Any length of boom may be used. if it is desired to lower the chain directly over the side of a ship, boat or barge, the boom may be eliminated, and the apparatus used as a Windlass with support 81 mounted to extend over the side at the guriwale of the vessel.

The davit has been described with hydraulic motors for movements of chain 88 and with a control system for imposing drag to keep the chain tensioned during 1 chain movements in both directions. A modification will now be described wherein electric motors are used instead of hydraulic motors. Referring again to the drawings, motors 78, 91-92 and 94-95, which drive sprockets 70, and 93, respectively, are electric motors in this embodiment. Because of speed control considerations, the motors are preferably direct current motors. In order to achieve the chain tensioning achieved with the embodiment having hydraulic motors, at least one of the last or trailing electric motors, with respect to the direction of chain travel, is either energized to operate after the other electric motors have been energized to operate, or is at least initially operated at slower speed, in order that drag and resultant chain tension will result. Control apparatus in connection with this operation of the electric motors is well within the ability of a person skilled in the art and need not be further described.

While a preferred embodiment of the invention has been shown in the drawings and described, many modifications thereof may be made by persons skilled in the art without departing from the spirit of the invention, and it is intended to protect by Letters Patent all forms of the invention fallingwithin the scope of the following claims.

1 claim: 7

1. Crane, comprising a longitudinal boom supported at its inner end, first chain drive means adjacent said inner end of said boom, second chain drive means at the outer end of said boom, chain means extending under tension between said first and second chain drive ond chain drive means, with respect to the direction of chain travel, upon starting the chain means in movement in either direction, whereby slack cannot develop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectable to an object to be supported or pulled by the crane.

2. The combination of claim 1, said boom extending from a floating vesseL' 3. The combination of claim 1, said first and second chain drive means comprising fluid motor means, said control means controlling the driving fluid supplied to said fluid motor means.

4. The combination of claim 1, said second chain drive means including sprocket means having said chain means engaged therewith, said sprocket means being swivel mounted whereby said portion of said chain means extending therebeyond may be directioned angularly to either side of said sprocket;

5. Crane, comprising a longitudinal boom supported at its inner end, first fluid motor chain drive means adjacent said inner end of said'boom, secondfluid motor chain drive means at the outer end of said boom, chain means extending under tension between said firstand second chain drive means and extending at its inner and outer ends beyond said first and second chain drive means, said first and second chain drive means being operable to move said chain means longitudinally in either direction, control means controlling the driving fluid supplied to said first and second drive means for automatically delaying starting in operation of the trailing one of said first and second chain drive means with respect to the direction of chain travel upon starting the chain means in movement in either direction by preventing hydraulic flud flow through the trailing fluid motor means until the pressure of hydraulic fluid reaches a certain magnitude, whereby said chain means is held against movement until the hydraulic fluid pressure reaches said certain magnitude, the leading fluid motor means being prevented from operating by the chain means being held against movement as described until said trailing fluid motor commences operating whereby slack cannot delelop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectable to an object to be supported or pulled by the crane.

6. The combination of claim 5, said control means comprising valve means which restrains hydraulic fluid flow to the trailing fluid motor means until the pressure reaches said certain magnitude.

7. The combination of claim 6, including additional chain drive means, comprising additional fluid motor means disposed to drive said chain means between said first and second chain drive means, said additional chain drive means being prevented from operating by the chain means being held against movement in the same manner as said leading chain drive means.

8. The combination of claim 7, including means for pivotally raising the lowering said boom, and including means for rotating said boom to change its direction.

9. The combination of claim 8, said boom extending from a floating vessel.

10. Crane, comprising a longitudinal boom supported at its innerend, first chain drive means adjacent said inner end of said boom, second chain drive means at the outer end of said boom, chain means extending under tension between said first and second chain drive means and extending at its inner and outer ends beyond said first and second chain drive means, said first and second chain drive means being operable to move said chain means longitudinally in either direction while maintaining said chain means tensioned therebetween, said second chain drive means including sprocket means having said chain means engaged therewith, said sprocket means being swivel mounted whereby said portion of said chain means extending therebeyond may be directioned angularly to either side of said sprocket, and including control means for automatically delaying starting in operation of the trailing one of said first and second chain drive means, with respect to the direction of chain travel, upon starting the chain means in movement in either direction, whereby slack cannot develop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectable to an object to be supported orpulled by the crane.

11. The combination of claim 10, said first and second chain drive means comprising fluid motor means, said control means controlling the driving fluid supplied to said fluid motor means.

12. The combination of claim 11, said control means preventing hydraulic fluid flow through the trailing fluid motor means until the pressure of hydraulic fluid reaches a certain magnitude, whereby said chain means is held against movement until the hydraulic fluid pressure reaches said certain magnitude, the leading fluid motor means being prevented from operating by the chain means being held against movement as described until said trailing fluid motor commences operating.

13. The combination of claim 12, said control means comprising valve means which restrains hydraulic fluid flow to the trailing fluid motor means until the pressure reaches said certain magnitude.

14. The combination of claim 13, including additional chain drive means, comprising additional fluid motor means, disposed to drive said chain means between said first and second chain drive means, said additional chain drive means being prevented from operating by the chain means being held against movement in the same manner as said leading chain drive means.

15. The combination of claim 14, including means for pivotally raising and lowering said boom, and including means for rotating said boom to change its direction.

16. Windlass, comprising a first chain drive means disposed upon-a support and spaced from an edge of said support, second chain drive means disposed to extend over said edge of said support, chain means extending under tension between said first and second chain drive means and extending at its inner and outer ends beyond said first and second chain drive means, said first and second chain drive means each being operable to move said chain means longitudinally in either direction while maintaining said chain means tensioned therebetween, control means for automatically delaying starting in operation of the trailing one of said first and second chain drive means, with respect to the direction of chain travel, upon starting the chain means in movement in either direction, whereby slack cannot develop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectableto an object to be suppoted or pulled by the windlass.

17. The combination of claim 16, said support comprising a floating vessel.

18. The combination of claim 16, said first and second chain drive means comprising fluid motor means, said control means controlling the driving fluid supplied to said fluid motors.

19. The combination of claim 16, said second chain drive means including sprocket means having said chain means engaged therewith, said sprocket means being swivel mounted whereby said portion of said chain means extending therebeyond may be directioned angularly to either side of said sprocket.

20. Windlass, comprising a first fluid motor chain drive means disposed upon a support and spaced from an edge of said support, second fluid motor chain drive means disposed to extend over said edge of said support, chain means extending under tension between said first and second chain drive means and extending at its inner and outer ends beyond said first and second chain drive means, said first and second chain drive means being operable to move said chain means longitudinally in either direction, control means controlling the driving fluid supplied to said fluid motors for automatically delaying starting in operation of the trailing one of said first and second chain drive means, with respect to the direction of chain travel, upon starting the chain means in movement in either direction by preventing hydraulic fluid flow through the trailing fluid motor means until the pressure of hydraulic fluid reaches a certain magnitude, whereby said chain means is held against movement until the hydraulic fluid pressure reached said certain magnitude, the leading fluid motor means being prevented from operating by the chain means being held against movement as described until said trailing fluid motor commences operating whereby slack cannot develop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectable to an object to be supported or pulled by the windlass.

21. The combination to claim 20, said control means comprising valve means which restrains hydraulic fluid .flow to the trailing flud motor means until the pressure reaches said certain magnitude.

22. The combination of claim 21, including additional chain drive means, comprising additional fluid motor means, disposed to drive said chain means between said first and second chain drive means, said additional chain drive means being prevented from operating by the chain means being held against movement in the same manner as said leading chain drive means.

23. The combination of claim 22, said support being a floating vessel.

24. Windlass, comprising a first chain drive means disposed upon a support and spaced from an edge of said support, second chain drive means disposed to extend over said edge of said support, chain means extending under tension between said firstand second chain drive means and extending at its inner and outer ends beyond said first and second chain drive means, said first and second chain drive means being operable to move said chain means longitudinally in either direction while maintaining said chain means tensioned therebetween, said second chain drive means including sprocket means having said chain means engaged therewith, said sprocket means being swivel mounted 7 whereby said portion of said chain means extending therebeyond may be directioned angularly to either side of said sprocket, control means for automatically delaying starting in operation of the trailing one of said first and second chain drive means, with respect to the direction of chain travel, upon starting the chain means in movement in either direction, whereby slack cannot develop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectable to an object to be supported or pulled by the windlass.

25. The combination of claim 24, said first and second chain drive means comprising fluid motor means, said control means controlling the drive fluid supplied to said fluid motors.

26. The combination of claim 25, said support being a floating vessel. 

1. Crane, comprising a longitudinal boom supported at its inner end, first chain drive means adjacent said inner end of said boom, second chain drive means at the outer end of said boom, chain means extending under tension between said first and second chain drive means and extending at its inner and outer ends beyond said first and second chain drive means, said first and second chain drive means each being operable to move said chain means longitudinally in either direction while maintaining said chain means tensioned therebetween, control means for automatically delaying starting iN operation of the trailing one of said first and second chain drive means, with respect to the direction of chain travel, upon starting the chain means in movement in either direction, whereby slack cannot develop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectable to an object to be supported or pulled by the crane.
 2. The combination of claim 1, said boom extending from a floating vessel.
 3. The combination of claim 1, said first and second chain drive means comprising fluid motor means, said control means controlling the driving fluid supplied to said fluid motor means.
 4. The combination of claim 1, said second chain drive means including sprocket means having said chain means engaged therewith, said sprocket means being swivel mounted whereby said portion of said chain means extending therebeyond may be directioned angularly to either side of said sprocket.
 5. Crane, comprising a longitudinal boom supported at its inner end, first fluid motor chain drive means adjacent said inner end of said boom, second fluid motor chain drive means at the outer end of said boom, chain means extending under tension between said first and second chain drive means and extending at its inner and outer ends beyond said first and second chain drive means, said first and second chain drive means being operable to move said chain means longitudinally in either direction, control means controlling the driving fluid supplied to said first and second drive means for automatically delaying starting in operation of the trailing one of said first and second chain drive means with respect to the direction of chain travel upon starting the chain means in movement in either direction by preventing hydraulic flud flow through the trailing fluid motor means until the pressure of hydraulic fluid reaches a certain magnitude, whereby said chain means is held against movement until the hydraulic fluid pressure reaches said certain magnitude, the leading fluid motor means being prevented from operating by the chain means being held against movement as described until said trailing fluid motor commences operating whereby slack cannot delelop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectable to an object to be supported or pulled by the crane.
 6. The combination of claim 5, said control means comprising valve means which restrains hydraulic fluid flow to the trailing fluid motor means until the pressure reaches said certain magnitude.
 7. The combination of claim 6, including additional chain drive means, comprising additional fluid motor means disposed to drive said chain means between said first and second chain drive means, said additional chain drive means being prevented from operating by the chain means being held against movement in the same manner as said leading chain drive means.
 8. The combination of claim 7, including means for pivotally raising the lowering said boom, and including means for rotating said boom to change its direction.
 9. The combination of claim 8, said boom extending from a floating vessel.
 10. Crane, comprising a longitudinal boom supported at its inner end, first chain drive means adjacent said inner end of said boom, second chain drive means at the outer end of said boom, chain means extending under tension between said first and second chain drive means and extending at its inner and outer ends beyond said first and second chain drive means, said first and second chain drive means being operable to move said chain means longitudinally in either direction while maintaining said chain means tensioned therebetween, said second chain drive means including sprocket means having said chain means engaged therewith, said sprocket means being swivel mounted whereby said portion of said chain means exTending therebeyond may be directioned angularly to either side of said sprocket, and including control means for automatically delaying starting in operation of the trailing one of said first and second chain drive means, with respect to the direction of chain travel, upon starting the chain means in movement in either direction, whereby slack cannot develop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectable to an object to be supported or pulled by the crane.
 11. The combination of claim 10, said first and second chain drive means comprising fluid motor means, said control means controlling the driving fluid supplied to said fluid motor means.
 12. The combination of claim 11, said control means preventing hydraulic fluid flow through the trailing fluid motor means until the pressure of hydraulic fluid reaches a certain magnitude, whereby said chain means is held against movement until the hydraulic fluid pressure reaches said certain magnitude, the leading fluid motor means being prevented from operating by the chain means being held against movement as described until said trailing fluid motor commences operating.
 13. The combination of claim 12, said control means comprising valve means which restrains hydraulic fluid flow to the trailing fluid motor means until the pressure reaches said certain magnitude.
 14. The combination of claim 13, including additional chain drive means, comprising additional fluid motor means, disposed to drive said chain means between said first and second chain drive means, said additional chain drive means being prevented from operating by the chain means being held against movement in the same manner as said leading chain drive means.
 15. The combination of claim 14, including means for pivotally raising and lowering said boom, and including means for rotating said boom to change its direction.
 16. Windlass, comprising a first chain drive means disposed upon a support and spaced from an edge of said support, second chain drive means disposed to extend over said edge of said support, chain means extending under tension between said first and second chain drive means and extending at its inner and outer ends beyond said first and second chain drive means, said first and second chain drive means each being operable to move said chain means longitudinally in either direction while maintaining said chain means tensioned therebetween, control means for automatically delaying starting in operation of the trailing one of said first and second chain drive means, with respect to the direction of chain travel, upon starting the chain means in movement in either direction, whereby slack cannot develop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectable to an object to be suppoted or pulled by the windlass.
 17. The combination of claim 16, said support comprising a floating vessel.
 18. The combination of claim 16, said first and second chain drive means comprising fluid motor means, said control means controlling the driving fluid supplied to said fluid motors.
 19. The combination of claim 16, said second chain drive means including sprocket means having said chain means engaged therewith, said sprocket means being swivel mounted whereby said portion of said chain means extending therebeyond may be directioned angularly to either side of said sprocket.
 20. Windlass, comprising a first fluid motor chain drive means disposed upon a support and spaced from an edge of said support, second fluid motor chain drive means disposed to extend over said edge of said support, chain means extending under tension between said first and second chain drive means and extending at its inner and outer ends beyond said first and second chain drive means, said first and second chain drive means being operable to move said chain means longitudinally in either direction, control means controlling the driving fluid supplied to said fluid motors for automatically delaying starting in operation of the trailing one of said first and second chain drive means, with respect to the direction of chain travel, upon starting the chain means in movement in either direction by preventing hydraulic fluid flow through the trailing fluid motor means until the pressure of hydraulic fluid reaches a certain magnitude, whereby said chain means is held against movement until the hydraulic fluid pressure reached said certain magnitude, the leading fluid motor means being prevented from operating by the chain means being held against movement as described until said trailing fluid motor commences operating whereby slack cannot develop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectable to an object to be supported or pulled by the windlass.
 21. The combination fo claim 20, said control means comprising valve means which restrains hydraulic fluid flow to the trailing flud motor means until the pressure reaches said certain magnitude.
 22. The combination of claim 21, including additional chain drive means, comprising additional fluid motor means, disposed to drive said chain means between said first and second chain drive means, said additional chain drive means being prevented from operating by the chain means being held against movement in the same manner as said leading chain drive means.
 23. The combination of claim 22, said support being a floating vessel.
 24. Windlass, comprising a first chain drive means disposed upon a support and spaced from an edge of said support, second chain drive means disposed to extend over said edge of said support, chain means extending under tension between said first and second chain drive means and extending at its inner and outer ends beyond said first and second chain drive means, said first and second chain drive means being operable to move said chain means longitudinally in either direction while maintaining said chain means tensioned therebetween, said second chain drive means including sprocket means having said chain means engaged therewith, said sprocket means being swivel mounted whereby said portion of said chain means extending therebeyond may be directioned angularly to either side of said sprocket, control means for automatically delaying starting in operation of the trailing one of said first and second chain drive means, with respect to the direction of chain travel, upon starting the chain means in movement in either direction, whereby slack cannot develop in the chain means and the chain means will continuously be maintained tensioned, the portion of said chain means extending beyond said second chain drive means being connectable to an object to be supported or pulled by the windlass.
 25. The combination of claim 24, said first and second chain drive means comprising fluid motor means, said control means controlling the drive fluid supplied to said fluid motors.
 26. The combination of claim 25, said support being a floating vessel. 